Your memory may quick fill up. Its recommended to remove the video from the phone after you have uploaded it in the group.
Its recommended to change a low video resolution, otherwise the video will be heavy to upload and will take long . Typical video resolutions in smartphones are HD and FULL HD, both are way too heavy, your video file will be close to 1GB with those resolutions. Recommended resolutions are either VGA (640x480) or QVGA (320x240) QVGA being the most lightweight (5min video fits in 50MB file)
If you record the video with your selfie camera, notice where the camera lense is located. Usually it is located on the top of the screen. Your eyes will be seen better in the video, if you watch straight to the lense instead of watching the screen.
When you record outdoor in a standing position, a selfie stick may become handy